In certain manufacturing processes, a device or component of a device may be cast or molded. For example, a molten material, such as a molten metal, may be poured into a mold and cooled to form the device or component in question. In certain casting systems, an elongated columnar structure may be produced that has multiple unidirectional crystals aligned substantially parallel, such as to an axis of the casting. The aligned crystal structure of a device produced from such systems may have crystal grain boundaries where faults or breaks may occur. In other directional casting systems, a single crystal device may be made that contains no grain boundaries, thereby enhancing the strength of the device. Such a single crystal device may be produced using a method of directional solidification for cooling the casting. Using directional solidification, a desired single crystal growth structure is created, typically at the base of a vertically disposed mold defining a device. The crystal growth structure then grows from the base to the top of the mold as molten metal in the mold solidifies.
Liquid metal cooled directional solidification processes may be used with directional solidification systems to create such a single crystal structure. For example, a mold may be filled with a molten metal while the mold is in a furnace. The furnace may include an induction coil or resistance heater to maintain the heat of the furnace. The mold may then be lowered into a liquid metal bath. The molten metal in the mold becomes solidified in the liquid metal bath due to the large thermal gradient between the mold (including the molten metal) and the liquid metal bath. The mold first solidifies into a crystal structure at the base of the mold, and then the crystal grows as more molten metal solidifies. The speed of solidification is controlled by how fast the mold is moved from the furnace into the liquid metal bath. To create the single crystal structure, the mold is lowered into the liquid metal bath at a specific, controlled rate. However, due to the temperature extremes and gradients involved, while in the liquid metal bath, the mold may crack and metal from the liquid metal bath may contact the device being formed, thereby causing imperfections to form on the device (e.g., pits in the metal of the device). Such manufacturing defects may result in a formed product being unusable or unacceptable for its intended purpose.